Phy 131 - Assignment 13
A. ∑Q = 0
(m c ΔT)tea + (mLf + m c ΔT)ice = 0
The tea just changes temperature. The ice changes state and changes
temperature.
mtea: 1 liter = 1000 ml = 1000 cm3, and water has a density of 1 g/cm3.
Tea is basically water, so its specific heat is cwater =
Above 0°, the ice has melted. So, its specific heat is also water’s, not ice’s.
(1000 g)(
)(10° - 30°) + m(
)+m(
)(10° - 0°) = 0
- 20 000 + 79.6 m + 10 m = 0
89.6 m = 20 000
m=
223 g
B. 1. a. Conduction & convection. Heat can’t flow by collisions of air molecules
that aren’t there, or by the circulation of air that isn’t there.
b. Radiation. A shiny surface not only absorbs radiation poorly, it also emits it
poorly. (So, it doesn’t let energy in or out.)
2.
C. 1. The steam gives off a large amount of heat as it condenses. For example, 1/10
gram of water cooling from 100°C to 30°C (the temperature of your hand) gives off
m c ΔT = 7 calories. But 1/10 gram of 100°C steam gives off mLv + m c ΔT = 61
calories.
2. ∑Q = 0
(m c ΔT)iron + (m c ΔT)water = 0
(1.5 kg)(
)(Tf - 600°) + (20 kg)(
672 Tf – 403 200 + 83 720 Tf – 2 093 000 = 0
84 393 Tf = 2 496 200
Tf =
29.6°C
)( Tf - 25°) = 0
D.
E. 1. The alcohol’s temperature will increase about twice as much as the water’s.
2.
F.1. Glass has a much lower thermal conductivity than metal, so heat flows along
that rod much slower. (A popular wrong answer is that glass has a lower specific
heat. The specific heat of glass is actually similar to aluminum’s.)
2.